The evaluation of the mutagenic activity of mainstream cigarette smoke is mostly based on studies with condensates or extracts in the standard Ames assay. Due to the methodological difficulties of testing air contaminants in their natural gaseous or aerosolised state, there are no accepted concepts and techniques for effective exposure of bacteria under such conditions. Therefore, we established a novel approach using an exposure device based on the cell exposure system CULTEX^®, which was connected to a smoking machine (smoking robot VC10). This allows us the investigation of chemically and physically unchanged mainstream cigarette smoke by exposing bacteria of Salmonella typhimurium strains directly to diluted mainstream smoke of the research cigarette K2R4F. In preliminary experiments the treatment of strain TA98 to whole smoke resulted in the induction of revertants dependent on dilution and the number of cigarettes smoked, whereas the gas phase induced no mutagenic signal. In comparison to studies with condensates by using the plate incorporation assay, the exposure of the bacteria directly to native cigarette mainstream smoke seems to enhance the susceptibility of the bacteria to mutation. The introduction of our exposure device in the field of inhalation genotoxicology offers new possibilities in the evaluation of genotoxicity in the Ames assay by taking in consideration not only hydrophilic but also hydrophobic substances in the particulate and gas phase.